Unambiguous detection of signal channels in optically amplified systems is necessary for performance monitoring, and to initiate corrective action in case of system failures. Reliable distinction of signal channels from optical amplifier noise is particularly critical for fast suppression of amplifier transients if the signal channels of a system are lost due to a fiber cut or some other failure. In addition, the continuous monitoring of optical amplifier performance to detect and localize degradations or faults before they affect service provides significant savings in the operation costs of optically amplified networks.
Currently, optical performance monitoring is accomplished using various sophisticated detectors, such as optical spectrum analyzers (OSAs) and optical channel monitors (OMONs). OSAs and OMONs may be used to detect changes of optical signal-to-noise ratios, either quantitatively by exact calibration, or by trend analysis over time. However, even in their most rudimentary and scaled-down form, these OSA and OMON devices are bulky and relatively expensive.